The present invention relates to an apparatus and methods for resisting thrust loads on a crane. More specifically, the present invention relates to a bearing system for resisting radial (i.e., horizontal) thrust loads from a boom on a post crane.
Ships and offshore platforms need cranes to rapidly and safely load and off-load various material and personnel. Affixable, pedestal-type cranes with a center post have been very popular in marine type applications. On a post crane, the superstructure and boom of the crane rotate on bearings about the axis of the post.
The post serves as the crane's structural base for resisting the thrust loads and overturning moments experienced by the crane. The thrust loads are transferred from the boom to the post via the bearings on which the superstructure rotates about the axis of the post. Specifically, vertical thrust loads are transferred from the boom to the post via a container ring bearing, which comprises a plurality of rollers. Radial (i.e., horizontal) thrust loads are transferred from the boom to the post via the radial bearing ring comprising a plurality of rollers, which rollably engage the outer circumference of the post.
While the post crane has many advantages over other types of cranes in a marine environment, the ability to achieve equal bearing loading about the bearings, especially the radial bearing ring, has been challenging. Failure to achieve equal loading about the bearings can result in uneven bearing roller wear, which can lead to premature repairs and downtime for the crane or even catastrophic failure of the crane.
To achieve equal roller loading about the radial bearing ring, manufacturers have had to rely on precision machining of the bearing ring and its rollers or structures that permit elastic deflections. Both options are less than desirable due to their expense. Also, the commercially available precision bearings with integral rings are limited in size to 6.5 meters in diameter, which in turn limits the load capacity of the crane. There is a need in the art for a more cost effective means of achieving equal roller loading about the radial bearing ring.